Fibers used in the preparation of reinforced plastics are sometimes pre-coated with a resin before being used as reinforcement. Such a resin coating is typically first applied to the fiber by various methods such as by the solution or molten coating of fiber with a curable composition followed by partially curing the coated fiber composite.
The usual purpose of the preliminary partial curing is to create a relatively dry handling and pliable fiber. A woven or random strand mat, or sheet, is typically then prepared from the coated fiber composite. The mat, or sheet, can later be molded by itself or with additional resin, during which additional curing takes place, to create a final, molded article.
A resin impregnation of fiber is disclosed for example, in U.S. Pat. No. 3,384,505 where a dry wound roll of continuous fiber or filament is placed in a vessel, a vacuum drawn to remove entrapped air in the roll and the roll then submerged in a liquid containing a heat curable, thermo-setting, composition which is initially free of cross-linking. Pressure is applied until the resin medium of resin catalyst and solvent has essentially filled the voids in the roll.
The patent teaches that the roll is removed from the remaining unabsorbed resin medium and heated to convert the resin to a partially cured state. The heating is taught to also tend to remove all or most of the solvents which were present in the original resin medium. By this method, the patent teaches, the fiber does not have to be unwound from its roll in order to be resin impregnated.
The patent more specifically teaches to treat glass fiber, wound in a roll, with an epoxy in solution of a solvent, such as for example, acetone, containing a catalyst or curative for the epoxy such as, for example, an amine. It is taught that the solvent should be present in an amount of about 10-300 weight percent of resin and curative.
However, it has been observed that when a dry, wound roll of continuous glass filament was submerged in an acetone solution of an epoxy containing an amine curative following by drying and curing the epoxy coating on the glass filament in accordance with such teaching, the curing was not controllable due to insulated exothermic reaction inside the roll even with refrigeration and the resultant coated, overcured (impregnated) glass filament was difficult to further process into a reinforced plastic product.
Thus, it is desired to have a method which can provide an epoxy coated fiber composite under controlled conditions.
In addition it is desired, for a number of composite plastic applications, that filaments be provided with an extremely small amount or very light coating of partilly cured epoxy thereon for the purpose of stabilizing the filaments. This is referred to herein as "sizing the filament" with a "sizing amount" of partially curved epoxy resin on the filament. The usual purpose is to provide "strand integrity" under controlled conditions.